Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.
There are multiple formulations known for use in HIV treatment therapy. The active substance Ritonavir [NORVIR soft gelatin capsule] is characterized by low aqueous solubility, a lack of bioavailability when given in the solid state, instability once in solution under ambient conditions and a metallic taste. U.S. Pat. No. 5,484,801 discloses a formulation wherein Ritonavir formulation has been optimized with respect to the vehicle, which essentially is a solvent comprising a mixture of (1) (a) a solvent selected from propylene glycol and polyethylene glycol or (b) a solvent selected from polyoxyethyleneglycerol triricinoleate, polyethylene glycol 40 hydrogenated castor oil, fractionated coconut oil, polyoxyethylene (20) sorbitan monooleate and 2-(2-ethoxyethoxy) ethanol or (c) a mixture thereof and (2) ethanol or propylene glycol to improve the bioavailability.
Whereas Kaletra® is a formulation of two HIV protease inhibitors [Lopinavir and Ritonavir] in a single formulation. Till recently, this formulation was available in a soft gel capsule, embodied in the U.S. Pat. No. 6,458,818 granted to Abbott. The patent covers a solution of Lopinavir and Ritonavir in a long chain fatty acid organic solvent. This soft gel formulation has been criticized due to stability problems and need for keeping the formulation in refrigerated condition. Abbott has now introduced a new tablet formulation for combined administration of Lopinavir and Ritonavir, instead of the previously known soft gel formulation. It has also filed patent applications related to this tablet formulation. For instance, WO2005039551 covers a combination of Lopinavir and Ritonavir in a water soluble polymer and surfactant wherein the tablet is formulated by melt extrusion process. Specifically, the disclosed process comprises following steps:                a) preparing a mixture of combination HIV protease inhibitors, a water-soluble polymer and a surfactant,        b) feeding the mixture in a twin screw extruder while maintaining a high temperature [133° C.] to form a homogeneous melt,        c) feeding this melt to a calendar with counter rotating rollers to be pressed into tablets.        
HIV therapy formulations need to be made in the most economical manner thereby reducing the final prices for AIDS patients across the world, especially in third world and developing countries. The above formulation and related melt extrusion process on account of its requiring expensive extrusion machinery & use of multiple surfactants [N Vinyl pyrrolidone and Sorbitan monolaureate or polyoxyethyleneglycerol oxystearate] may not necessarily result in an economical formulation. Also, since the disclosed process requires heating the drug constituents to high temperatures [exceeding 100° C.] it may possibly result in degradation of the drug constituents.